Neuroscience has become to contemporary novelists what psychoanalysis was to a previous generation - the cutting edge of exploration into the novel's elemental concerns: consciousness, identity, memory, the locus of the self. Umberto Eco, in his fifth novel, uses it as the starting point for a profound study of the influences that shape and determine a life, though he quickly leaves the science behind and moves into the more familiar terrain of history and literature.

Approaching 60, Giambattista Bodoni, known as Yambo, a Milanese antiquarian book dealer, has been plunged by a sudden attack into a brief coma, from which he emerges with his autobiographical memory entirely missing. The memories of a lifetime of reading, however, remain intact, and his mind is a fog of fragmented quotations and encyclopaedic facts.

Amnesia, as a pretext for analysing how the narrative of our selves is created by editing or fictionalising memories, is a well-used trope in literature and film, but Eco fully humanises Yambo's anguish at the dream-like quality of his life. In the first part of the novel this is beautifully realised in his encounters with his beautiful young assistant, Sibilla. His friend has made a sly but unspecific comment about her, and now Yambo has no idea about their previous relationship. Did they have an affair, or did he once make a clumsy pass at her, or has he simply admired her from a distance while maintaining a professional appearance, or none of these? His dilemma is exquisitely agonising, and emphasises the fictive nature of love at the best of times. 'The best part of having loved, I told myself, is the memory of having loved. But to think you have loved, yet not be able to recall it?'

One of the children's stories Yambo remembers is that of Signor Pipino, 'born an old man and died a bambino'. Yambo too has been born a tabula rasa, at 60, and must follow the course of his life backwards if he is to understand who he was. He returns to his grandfather's country estate, to which he was evacuated as a boy during the war, and there immerses himself in an attic full of his childhood reading matter, together with his grandfather's newspapers and magazines from the time of Mussolini and a collection of old records. Many of these images, such as a half-clad Josephine Baker, kindle the mysterious flames of the title, surges of recognition frustratingly divorced from context.

Through these books and songs, some of which are reproduced intriguingly in the text and illustrated plates, he pieces together a full history of war-time Italy, though only tantalising glimpses of his own part in it. This lengthy section is reminiscent of the long historical digressions of Eco's previous books, although here it appears meandering and plotless, often appearing as a self-indulgent catalogue of the author's boyhood reading.

But it is worth persisting with this section, and not just for its detailed picture of the Black Brigades and the partisan insurgency. It ends with another shocking discovery that precipitates a second attack; within his coma, his memory returns in overdrive, and all the clues are shaped in the final section into a compelling narrative of wartime heroics and first love. Eventually, this rush of memory becomes phantasmagoric, an apocalyptic vision couched in the language of Dante and the Book of Revelation, in which all the figures of fact and fiction appear to him in a Busby Berkeley dance of hyperreality, climaxing in a horror for which the reader is unprepared.

For all its vivid cartoons, this is a novel about fog, with a dark vision. What begins with the most advanced science of the mind ends with deliberate echoes of Calderón de la Barca's questions about dreams and reality, and confirms Eco as an outstanding writer of philosophy dressed as fiction.